Arrangement comprising a fuel cell system

ABSTRACT

A system ( 0 ) includes an electrical load system ( 54 ) with a load network battery ( 82 ), and a fuel cell system ( 1 ). Operation is simplified, especially during start of the fuel cell system ( 1 ) if the fuel cell system ( 1 ) has a system battery ( 56 ). A system voltage across the system battery ( 56 ) can be supplied to electrical system loads ( 80 ) of the fuel cell system ( 1 ) and, via a load voltage converter ( 77 ) and at least one additional voltage converter ( 86 ), to the load system ( 54 ) and secondary electrical loads ( 84, 85 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase Application ofInternational Application PCT/EP2012/063381 filed Jul. 9, 2012 andclaims the benefit of priority under 35 U.S.C. §119 of German PatentApplication DE 10 2011 079 104.3 filed Jul. 13, 2011, and German PatentApplication DE 10 2011 079 169.8 filed Jul. 14, 2011, and German PatentApplication DE 10 2011 088 563.3 filed Dec. 14, 2011, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an arrangement comprising a fuel cellsystem. The invention furthermore relates to such a fuel cell system.

BACKGROUND OF THE INVENTION

The use of fuel cells in different applications, for example in avehicle or a stationary application is thoroughly known. A fuel cellsystem thereby supplies electrical loads with electrical energy. To thisend, the fuel cell system comprises a fuel cell, which for example isformed as a stack. The fuel cell generates an electrical voltage makinguse of the chemical reaction of a cathode gas and an anode gas, whereinas cathode gas oxygen-containing gases, in particular air, are usuallyused, while hydrogen-containing gases are employed as anode gas as arule. In many applications, the fuel cell system is part of anarrangement, wherein the arrangement frequently comprises an electricalload system, in which different electrical loads or first loads aresupplied with an electrical voltage. To this end, the load systemcomprises in particular a load network battery. Here, as a rule, thevoltage of the load network and the electrical voltage generated by thefuel cell are at different voltage levels. In other words, this meansthat while a load network voltage of the load system, in particular ofthe load network battery, is at a load network voltage level, the cellvoltage of the fuel cell has a cell voltage level that differs from theload network voltage level. The fuel cell system itself comprises aplurality of electrical loads or system loads such as for example ablower, control valves and a control unit. Since the fuel cell during astarting operation of the fuel cell system cannot provide electricalenergy directly, the fuel cell system during the starting operationrequires an external energy supply for supplying the system loads.

Such a fuel cell system is known for example from DE 10 2009 030 236 A1.

SUMMARY OF THE INVENTION

The present invention deals with the problem of stating an improved orat least alternative embodiment for an arrangement comprising a fuelcell system, which is characterized in particular by an independentstarting of the fuel cell system.

According to the invention, an arrangement is provided comprising a fuelcell system and an electrical load system. The load system is for theelectrical supply of first loads and comprises a load network batterywith a load network voltage at a network load voltage level. The fuelcell system comprises a fuel cell for generating an electrical cellvoltage at a cell voltage level. The fuel cell system is for supplyingelectrical system loads of the fuel cell system and comprises a systembattery with a system voltage at a system voltage level. The loadnetwork load voltage level and the system voltage level are different.The fuel cell system comprises a voltage converter device for convertingthe cell voltage level to the system voltage level and/or of the systemvoltage level to the cell voltage level. For supplying electricalsecondary loads, at least one additional voltage converter is providedfor adapting the system voltage across the system battery to at leastone additional voltage level. The system voltage level and theadditional voltage level are different. For supplying the load system,at least one load voltage converter is provided for adapting the systemvoltage across the system battery to the load network voltage level.

The present invention is based on the general idea of equipping a fuelcell system of an arrangement with at least one system battery thatdiffers from a load network battery of a load system of the arrangement,wherein the system battery has an electrical system voltage at a systemvoltage level. In this case, the system battery functions in particularas a storage unit or as a buffer between a fuel cell of the fuel cellsystem and electrical loads of the fuel cell system or of thearrangement, wherein the fuel cell generates a cell voltage at a cellvoltage level by means of fuel cell elements. Supplementing the fuelcell system through the system battery now particularly results in thatthe system voltage made available by the system battery can be suppliedto system loads, i.e. electrical loads of the fuel cell system. Startingof the fuel cell system for example without supplying externalelectrical energy can thereby also be carried out. If the fuel cellsystem has a solid oxide fuel cell (SOFC), in particular heating-up ofthe constituent parts of the fuel cell system, in particular theheating-up of electrodes or an anode and/or a cathode of the fuel cell,during the starting operation is possible without external supply ofelectrical energy or the electrical energy required for the startingoperation is reduced. If the fuel cell system has a low-temperature fuelcell, for example PEM-fuel cell, the starting operation, in particularsupplying the system loads with electrical voltage, can be realizedwithout external supply of electrical energy. In addition, the systemvoltage can also be supplied to other electrical loads, in particularthe load system of the arrangement and thus first loads.

According to the inventive idea, the fuel cell system comprises avoltage converter device, which converts the cell voltage level to thesystem voltage level and/or the system voltage level to the cell voltagelevel. The voltage converter device thus serves in particular thepurpose of rendering the cell voltage generated by the fuel cellsuppliable to the system battery. Alternatively or additionally, thevoltage converter device can render the system voltage across the systembattery suppliable to the fuel cell. To this end, the voltage converterdevice is practically electrically connected to the fuel cell and thesystem battery, wherein the respective electrical connections do notnecessarily run directly from the voltage converter device to the fuelcell or to the system battery. This means in particular that otherdevices or components can be connected between the fuel cell, thevoltage converter device and the system battery. In this case, the termload system does not at all mean that the load system does not have anenergy supply or electrical voltage supply that is separate from thefuel cell system. The load system can rather comprise an energy supplythat differs from the fuel cell system or be connected to such asupplier.

The electrical connection with the fuel cell is preferentially andpractically realized by means of the electrodes of the fuel cell.Accordingly, the cell voltage is tapped off the electrodes of the systemvoltage preferentially supplied to the electrodes.

As system loads of the fuel cell system, an air supply device, a fuelsupply device, a heater, a control unit as well as a valve of the fuelcell system are exemplarily pointed out here.

To supply secondary electrical loads, i.e. also loads which do notbelong to the arrangement, the system battery is additionally connectedto at least one additional voltage converter, wherein the respectiveadditional voltage converter adapts the system voltage across the systembattery to an associated additional voltage level. The respectiveadditional voltage level can be above or below the system voltage. Therespective additional voltage converter makes available the associatedadditional voltage at the associated additional voltage level availableto the secondary load or the secondary loads, wherein the respectiveadditional voltage level is above or below the system voltage level.

For the electrical supply of the load network a load voltage converterthat is electrically connected to the system battery is additionallyprovided, which adapts the system voltage across the system battery tothe load network voltage level. The load voltage converter consequentlyserves the purpose of making the electrical voltage generated by thefuel cell system available to the load system. The load network voltagelevel is above or below the system voltage level, wherein the loadvoltage converter increases or reduces the system voltage level to theload network voltage level.

It is pointed out that the cell voltage generated by the fuel cell andthe system voltage across the system battery are d.c. voltages as arule. Accordingly and practically, the system loads are suitable foroperation with a d.c. voltage. Thus, the voltage converter devicepreferentially comprises at least one d.c. voltage converter, i.e. inparticular a so-called “DC/DC-converter”. If the load network voltage isalso a d.c. voltage, the load voltage converter can likewise comprisesuch a d.c. voltage converter.

It is noted, furthermore, that the fuel cell as a rule is formed as astack of fuel cell elements. The cell voltage of the fuel cell in aseries connection of the individual fuel cell elements is consequentlyobtained as the sum of the electrical voltage generated by theindividual fuel cell elements. If the cell voltage in an embodiment ofthe arrangement amounts to for example 42V and the respective fuel cellelement generates an electrical voltage of 0.7V, the fuel cell comprises60 fuel cell elements connected in series. The electrical voltagegenerated by the respective fuel cell however depends among other thingson the output, i.e. on a load. If the voltage of the respective fuelcell element with a full load for example drops to 0.6V, the cellvoltage accordingly is reduced to 36V. If the voltage of the respectivefuel cell system while idle, i.e. without load, increases to 1.0V, thecell voltage accordingly rises to 60V. The voltage converter device thusalso serves in particular the purpose of balancing these fluctuations ofthe cell voltage and converting the load-dependent cell voltage and thusthe load-dependent cell voltage system into the substantially constantsystem voltage level.

Preferred is an embodiment, in which the load network battery, similarto the system battery, functions as a storage unit or as a buffer, bymeans of which the first loads are electrically supplied.

According to a further preferred embodiment, the fuel cell systemcomprises an electrical charging device. The combustion engine serves inparticular the purpose of charging the system battery by means of theelectrical cell voltage generated by the fuel cell. The charging devicethus allows in particular storing the electrical energy generated by thefuel cell by means of the system battery. The electrical energy thusstored is now in particular during a starting operation of the fuel cellsystem suppliable to the system loads, by way of which a starting of thefuel cell system that is independent of the outside, i.e. independent ofexternal voltage or electrical energy suppliers is ensured. In thiscase, the charging device is preferentially arranged between the voltageconverter device and the system battery. The charging device can also bearranged within the voltage converter device or be part of the voltageconverter device. Alternatively, the charging device can also bearranged on the system battery or be a part of the system battery.

In a further preferred embodiment, at least one of the additionalvoltage converters comprises an inverter. At least one of the additionalvoltage converters is consequently designed in such a manner that itadapts the d.c. voltage-like system voltage across the system battery tothe corresponding additional voltage level and into an a.c. voltage.This now serves in particular for the electrical supply of secondaryloads, which are operated with an a.c. voltage. The secondary loads inthis case can be external loads, which are operated with usual domesticvoltages. The additional voltage thus amounts to in particular 220V or110V. As examples for such secondary loads, reference is made torefrigerators or cooler boxes, TV sets or displays as well aselectrically operated air-conditioning devices, in particularair-conditioning compressors.

The respective additional voltage levels can be both below as well asabove the system voltage level. Embodiments are conceivable for example,in which an additional voltage level each is above and an additionalvoltage level below the system voltage level. Accordingly, thearrangement comprises two additional voltage converters, wherein one ofthe additional voltage converters increases the system voltage level tothe first additional voltage level and thus renders the first additionalvoltage suppliable to first secondary loads while the second additionalvoltage converter reduces the system voltage level to the secondadditional voltage level, rendering it suppliable to the secondsecondary loads. Embodiments are also preferred, in which at least onesuch additional voltage converter increases the system voltage level toan additional voltage level with a high voltage. Such a high voltageserves for example for the operation of air-conditioning devices.

Embodiments are also conceivable, in which such an additional voltageconverter merely comprises an inverter of said type. This additionalvoltage converter also converts the system voltage across the systembattery merely into an a.c. voltage.

In a further preferred embodiment, the system voltage across the systembattery is suppliable to electrodes of the fuel cell and thus the anodeof the fuel cell. Supplying the system voltage across the system batteryto the fuel cell in particular serves the purpose of protecting theelectrodes and in particular the anode from oxidation. This so-called“protective voltage”, as is known for example from US 2002/0028362 A1,is practical in particular if the anode is exposed to oxidizingconditions. To this end, the fuel cell system, in particular the voltageconverter device, is designed in such a manner that the system voltageor the system voltage level is suppliable to the electrodes of the fuelcell. Supplying the system voltage to the electrodes or to the anode ispreferentially controllable and regulatable. Such a transfer of thesystem voltage to the electrodes can thus be activated and subsequentlydeactivated again in particular when required, for example during thestart or shutting down of the fuel cell system. The voltage converterdevice is additionally designed optionally in such a manner that it canconvert the system voltage at the system voltage level into anelectrical voltage at another electrical voltage level. This now servesthe purpose in particular of adapting the voltage to be supplied to theelectrodes to the respective conditions, in particular the oxidizingconditions on the anode side. To this end, the fuel cell systempreferentially comprises a device, which allows determining the relevantconditions on the electrodes and in particular on the anode side. Such adevice can in particular comprise a temperature measurement device and adevice for determining the oxygen concentration or the oxygen ionconcentration. In addition, a control device can be provided, whichregulates and controls the protective voltage independently of thecorresponding parameters.

It is pointed out that supplementing the fuel cell system through thevoltage converter device and the load voltage converter as well as theat least one additional voltage converter also increases the economy ofthe fuel cell system or the associated arrangement. This is the case inparticular because these constituent parts of the invention arethoroughly known and allow simple and cost-effective assembly orproduction.

In a preferred embodiment, the arrangement is part of a vehicle, inparticular of a motor vehicle. In this case, the load system cancorrespond to an electrical system of the vehicle. Thus, the first loadsare in particular control units, light bulbs as well as a radio of thevehicle. Consequently, the load network battery is a battery of themotor vehicle's electrical system. The cell voltage generated in anapplication in a vehicle as a rule is between 42 and 100V, while thesystem voltage preferentially has a value of 24V, as a consequence ofwhich the system loads are also operated at a system voltage level of24V. Furthermore, the voltage of the vehicle's electrical system as arule has a value of 12V, as a consequence of which the initial loads areoperated at a load network voltage level of 12V. In this case, thevoltage converter device converts the cell voltage generated by the fuelcell to the system voltage level of 24V and supplies the convertedvoltage to the system battery. Furthermore, the load voltage converterin this case converts the system voltage of 24V to the load networkvoltage level of 12V and supplies the converted voltage to the vehicle'selectrical system, in particular to the vehicle's electrical systembattery. The load voltage converter is thus designed in particular as astep-down converter. In this case, the vehicle's electrical systembattery functions similar to the system battery as a storage unit or asa buffer, out of which the first loads can be electrically supplied.Converting the system voltage to the high-voltage level or into an a.c.voltage through an additional voltage converter of the said type canserve for the operation of secondary loads with a corresponding voltagerequirement, such as for example an air-conditioning system of thevehicle or an air-conditioning compressor as well as a TV set. This ispossible in particular even when the vehicle, in particular an internalcombustion engine of the vehicle, is not operated and thus the fuel cellsystem ensures a corresponding supply of the loads. The furtheradditional voltage converter can additionally make available a usualdomestic voltage in order to operate for example a TV set, a coffeemaker etc.

It is clear that the values of the respective voltages or voltage levelsstated here do not constitute any restrictions of the present invention.Other values of the respective voltages are thus also conceivable.Furthermore, the respective voltage can also be an a.c. voltage withoutleaving the scope of this invention.

Such an arrangement can also be part of a stationary system. In thiscase, the system battery, as already mentioned, in particular serves forthe independent starting of the fuel cell system and for the purpose ofrendering the system voltage suppliable to the electrodes of the fuelcell, in particular as protective voltage.

The starting operation of the fuel cell system can be optimized if thefuel cell system comprises an additional burner which produces a warmadditional burner exhaust gas. The heat of the additional burner exhaustgas is in particular suppliable to a reformer of the fuel cell system,in particular during the staring operation or during a cold start.

In an advantageous further development, the fuel cell system comprisesthe reformer for generating and supplying a reformat gas, which issuppliable to the anode side by means of a reformat gas line. Fortransferring the heat of the additional burner exhaust gas to thereformer, the fuel cell system additionally comprises a reformer supplydevice. To this end, the reformer supply device is coupled to thereformer in particular in a heat-transferring manner. The heat transferdoes not necessarily take place through the additional burner exhaustgas entering the reformer. The heat transfer can also be realized inthat the additional burner exhaust gas flows past or around thereformer.

In a preferred embodiment, the reformer supply device comprises aninflow and a return. The inlet of the reformer supply device serves forsupplying the additional burner exhaust gas to the reformer, while thereturn of the reformer supply device serves for returning the additionalburner exhaust gas from the reformer. To this end, the inflow and thereturn are practically fluidically connected to one another, whereinthis connection is preferentially realized in the region of the reformeror in the vicinity of the reformer. In this case, the supply or thedischarge of the additional burner exhaust gas to or from the reformerdoes not necessarily mean that the additional burner exhaust gas entersthe reformer. Preferred are embodiments, in which the additional burnerexhaust gas flows past the outside of the reformer, i.e. in particularpast a housing of the reformer. Thus, a possible realization is to formthe inlet and/or the return of the reformer supply device in particularin the region of the reformer in the manner of a hose, arranging it onthe reformer in a covering manner.

According to a further preferred embodiment, the reformer is at leastpartially surrounded by a through-flow capable heating jacket. Thereformer is consequently and at least partially covered by thethrough-flow capable heating jacket. The heating jacket furthermore iscoupled to the reformer in a heat-transferring manner. To this end, theheating jacket is for example formed by a hollow body covering thereformer, wherein a wall of the heating jacket which is adjacent to thereformer contacts the reformer. Alternatively, an embodiment isconceivable, in which the housing of the reformer, in particular anouter wall of the reformer, forms an inner wall of the heating jacket.For realizing the through-flow capability, the heating jacket comprisesat least one opening, which serves as an inlet and/or an outlet.

The heating jacket is preferentially fluidically separated from thereformer. This means that a path of the additional burner exhaust gasheating the reformer is fluidically separated from a path of thereformat gas. This fluidic separation in this case also applies to eductfeeds to the reformer. This means in particular that a fuel supply tothe reformer or an oxidant gas supply to the reformer is in each casefluidically separated from the reformer supply device.

In an advantageous further development, the reformer supply device isfluidically connected to the through-flow capable heating jacket andthus transfers the heat of the additional burner exhaust gas to thereformer. To this end, the inflow and the return of the reformer supplydevice for example are fluidically connected to the through-flow capableheating jacket. These connections are preferentially realized via twoopenings of the heating jacket. This means that the inflow isfluidically connected to a first opening and the return is fluidicallyconnected to a second opening. The additional burner exhaust gas thusflows to the reformer or to the heating jacket via the inflow and viathe return away from the reformer or from the heating jacket, by way ofwhich a heat transfer to the reformer is ensured. If the openings of thereformer and thus the fluidic connections of the inflow or the returnwith the heating jacket are additionally arranged on opposite sides ofthe heating jacket, this results in an improved heat transfer on thereformer, since a path of the additional burner exhaust gas within theheating jacket is enlarged or maximized. To this end, the heatingjacket, in particular the cavity of the heating jacket, can be expandedwith guiding elements which define a predetermined path of theadditional burner exhaust gas. Obviously, the heating jacket can alsocomprise a plurality of first openings and/or a plurality of secondopenings, each of which are fluidically connected to the inflow or thereturn.

For feeding a cathode gas or a fuel cell air to the cathode side of thefuel cell, the fuel cell system with a further embodiment comprises afuel cell air line. In order to render the heat of the additional burnerexhaust gas also suppliable to the cathode gas, the fuel cell systemwith a preferred embodiment comprises an additional burner heat transferdevice. The additional burner heat transfer device is coupled in aheat-transferring manner to an additional burner exhaust line or simplyadditional exhaust line or arranged within the additional exhaust lineand additionally connected to the fuel cell air line in aheat-transferring manner. The additional exhaust line serves fordischarging the additional burner exhaust gas produced by the additionalburner. The additional exhaust line accordingly discharges in particulara part of the additional burner exhaust gases, which is not utilized forheating the reformer and/or the additional burner exhaust gas returnedfrom the reformer.

In a further preferred embodiment, the reformer in its interiorcomprises a mixing chamber and a catalytic converter adjacent to themixing chamber. In the mixing chamber, a reformer fuel is mixed withreformer air and combusted or preheated, while the conversion of themixture into the reformat gas by means of the catalytic converter takesplace. Practically, the mixing chamber is arranged upstream of thecatalytic converter. Preferably, the heating jacket surrounds thereformer in the region of the catalytic converter and thus warms orheats predominantly the catalytic converter. Consequently, the mixingchamber during the process is heated through the heat transfer from thecatalytic converter or through the heat transfer of the regionsurrounding the heating jacket.

According to a further embodiment, a mixing jacket surrounds thereformer in the region of the mixing chamber. The mixing jacket isadditionally fluidically connected to a reformer air line for supplyingthe reformer with reformer air. The mixing jacket serves for thepreconditioning of the reformer air and is practically fluidicallyconnected to the reformer, in particular the mixing chamber. Thisfluidic connection is realized by means of at least one mixing jacketoutlet, which is arranged on the inside of the mixing jacket facing thereformer or the mixing chamber. Accordingly, the fluidic connection canbe realized with the reformer air line on the outside of the mixingjacket facing away from the reformer or from the mixing chamber.Preferably, the mixing jacket comprises a plurality of mixing jacketoutlets, which are evenly distributed along the circumferentialdirection of the reformer or of the mixing chamber, so that the reformerair evenly or homogenously flows into the mixing chamber.

In its interior, the reformer can also comprise an evaporator space,which is arranged on the side of the mixing chamber facing away from thecatalytic converter or upstream of the mixing chamber. The evaporatorspace serves for evaporating the mostly liquid fuel and is practicallyfluidically connected to a fuel line for supplying the fuel to thereformer.

Preferred is an embodiment, in which the inflow of the reformer supplydevice on the one hand is fluidically connected to the additionalexhaust line and on the other hand to the through-flow capable heatingjacket covering the reformer. The fluidic connection to the additionalexhaust line is preferentially realized upstream of the additionalburner heat transfer device, wherein the term upstream in this case isgiven here with respect to the flow direction of the additional burnerexhaust gas within the additional exhaust line. The inflow of thereformer supply device thus conducts the additional burner exhaust gasupstream of the additional burner heat transfer device to the reformer.Alternatively or additionally, the return of the reformer supply deviceis fluidically connected on the one hand to the heating jacket andfluidically connected on the other hand to the additional exhaust line.The fluidic connection between the return and the additional exhaustline is preferentially realized downstream of the additional burner heattransfer device. The return thus conducts the additional burner exhaustgas, in particular the additional burner exhaust gas supplied from theinflow, from the heating jacket or from the reformer back to theadditional exhaust line. In the process, embodiments are preferred, inwhich both the return as well as the inflow of the reformer supplydevice are realized in such a manner.

In an advantageous further development, the heat of the additionalburner exhaust gas can be supplied to the fuel cell. To this end, thefuel cell system can comprise a branch, which branches the additionalburner exhaust gas off the additional exhaust line, then conducting itback to the additional exhaust line. The branch is additionally coupledto the fuel cell in a heat-transferring manner. This heat-transferringcoupling is realized for example by means of an end plate or terminationplate of the fuel cell, which terminates the fuel cell and is coupled tothe branch in a heat-transferring manner.

The branching-off or return of the additional burner exhaust gas throughthe branch does not necessarily take place directly from the additionalexhaust line. In particular, the branch-off and/or the return can takeplace via the reformer supply device.

In a further embodiment, the fuel cell system in addition to said fuelline comprises a further fuel line, which supplies the additional burnerwith an additional burner fuel.

The fuels of the reformer and of the additional burner can generally bedifferent. However, preferred is an embodiment, in which the reformerfuel and the additional burner fuel are identical. Consequently, thereformer and the additional burners use or convert the same fuel.Practically and preferentially, the common fuel in this case can betaken from a common container, in particular a tank or a pressurevessel. The fuel additionally corresponds preferably to the fuel of aninternal combustion engine of a vehicle in or on which the fuel cellsystem is arranged.

The same applies to an air supply line for supplying the additionalburner with air as oxidant gas. This means, the oxidant gas of theadditional burner and the reformer air are identical and in particularair. In addition, the supply of the air to the additional burner or tothe reformer can take place through a common conveying device, forexample a pump.

It is pointed out that the additional burner can be practicallyregulatable or controllable. The additional burner is thus operable inparticular when required. Thus, the transfer of the heat of theadditional burner exhaust gas to the reformer takes place merely whenrequired, in particular during the starting operation of the fuel cellsystem. Accordingly, the additional burner can be switched off during anormal operation of the fuel cell system. In particular, a controldevice can be provided which controls or regulates the additionalburner. It is conceivable to additionally or optionally arrange a valvein the reformer supply device, which regulates a metering of the flow ofthe additional burner exhaust gas to the reformer, in particular to theheating jacket.

According to an operating method for the cold start of the fuel cellsystem, residual gas, which is contained in gas-carrying components ofthe fuel cell system, can be circulated from the anode side of the fuelcell to the reformer and from the reformer to the anode side, inparticular for as long as the anode or anode side of the fuel cell islocated below an anode limit temperature. In other words, in a sectionof the fuel cell system, residual gas is conveyed in a circuit betweenthe reformer and the anode side of the fuel cell. Since the fuel cellair which is preheated with the help of the additional burner heats upthe cathode side of the fuel cell, this automatically produces aheating-up of the anode side as well, so that a heat transfer to theresidual gas conveyed in the circuit takes place as well. Thiscirculating residual gas transports the heat to the transformer where itcauses a preheating of the reformer and in particular of the catalyticconverter of the reformer.

The starting procedure introduced here thus simultaneously realizes apreheating of the fuel cell and of the reformer with the help of theadditional burner. Because of this, the reformer becomes more quicklyready for operation which shortens the starting procedure as a whole,wherein at the same time a material-saving procedure is realized inorder to be able to avoid damaging the individual components due toelevated thermal loading.

By using the additional burner, a residual gas burner can for example bedesigned for a rated operation of the fuel cell, since the additionalburner can be switched off at the end of the cold start operation.Consequently, an improved efficiency is obtained for the rated operationof the fuel cell system.

According to an advantageous embodiment, the reformer can be operated atleast temporarily in a reformer operating state before reaching apredetermined (first) anode limit temperature, which for example can bearound approximately 250° C. Such a reformer operation can be realizedfor example at an adequately high temperature in that the reformer istemporarily supplied with fuel and reformer air at an appropriatefuel/air ratio. In this way, oxygen contained if appropriate in thecontinuously circulating residual gas can be converted or consumed. Itis important that during this temporary reformer operating state of thereformer, the residual gas continues to be circulated in a circuitbetween anode side and reformer. In this way, the entire oxygen gascontained in the residual gas can be reliably consumed. This temporaryreformer operating state is carried out in order to be able to continuecirculating the residual gas in the circuit even with risingtemperatures, without damage to the anode of the fuel cell occurring. Athigher temperatures, for example from 300° C., the danger of a lastingdamage of the anode through a contact with oxygen is increasedsignificantly.

In the case that a warm start of the reformer with immediate reformeroperating state should not be possible, a cold start of the reformer hasto be carried out, during which it is initially operated in a burneroperating state. According to a further development of the startingprocedure introduced here, the reformer can thus be operated in a burneroperating state that is below a predetermined limit temperature of thecatalytic converter of the reformer, wherein the reformer is suppliedwith reformer air and reformer exhaust gas formed in the reformer isdischarged via the exhaust line. The reformer then serves as additionalheat source, namely as an additional burner for heating up the catalyticconverter. As soon as the catalytic converter limit temperature is thenreached, which can be between 350° C. and 900° C., the operation of thereformer can be converted to the reformer operating state.

For as long as the temperature on the anode side is below a re-oxidationlimit, which can for example be at approximately 300° C., the gas comingfrom the reformer can be conducted through the anode side. Optionally,the gas coming from the reformer can be conducted through the exhaustline subject to bypassing the anode side, as a result of which a contactof the anode with the oxygen carried along in the gas coming from thereformer can be avoided.

Independently of whether the reformer exhaust gas flows through orbypasses the anode side, the reformer exhaust gas can be used forpreheating fuel cell air.

As soon as the catalytic converter of the reformer has reached itspredetermined operating temperature, which for example is around 900°C., the reformer can be operated particularly effectively in itsreformer operating state. The reformat gas usually contains no oxygenand can be conducted through the anode side, which additionally resultsin a heating-up of the fuel cell. In addition to this, the reformat gascan be converted in the residual gas burner together with the fuel cellair discharged from the cathode side, i.e. combusted, as a result ofwhich further heat is liberated, which can be utilized for preheatingthe fuel cell air.

The additional burner can now be deactivated as soon as the residual gasburner takes over the preheating of the fuel cell air or as soon as apredetermined (second) anode limit temperature or anode operatingtemperature is reached.

In another embodiment it can be provided to again switch off thereformer on reaching a predetermined further (third) anode limittemperature and to continue circulating the residual gas that is nowfree of oxygen between anode side and reformer. This third anode limittemperature is significantly below the second anode limit temperature orbelow the anode operating temperature. The third anode limit temperaturehowever is also above the first anode limit temperature. Below the anodeoperating temperature, which can be around 650° C., there is the risk ofsoot formation or soot deposits on the anode of the fuel cell. Byswitching off the reformer, this risk can be substantially reduced sincethe temperature range that is critical for the soot formation isbypassed.

According to an advantageous further development, the reformer can thenbe switched on again on reaching a predetermined further (fourth) anodelimit temperature and immediately operated in the reformer operatingstate. At any rate, the fourth anode limit temperature is higher thanthe third anode limit temperature. The third anode limit temperature canfor example be around 350° C. The fourth anode limit temperature can bearound approximately 650° C. It can therefore be selected in particularas high as the previously mentioned second anode limit temperature or asthe anode operating temperature. The renewed switching-on of thereformer in the presence of the fourth anode limit temperature makespossible a warm start of the reformer, i.e. an immediate operation ofthe reformer in the reformer operating state. At the comparatively hightemperatures present now, the risk of the soot formation or soot depositon the anode is substantially reduced.

As soon as the anode side or the fuel cell then reaches a minimumtemperature, the fuel cell can be put into service. The startingprocedure is then terminated.

According to another advantageous embodiment, air, for regulating atemperature of the fuel cell, can be directed from a bypass air line,which bypasses the residual gas heat transfer device arranged in thefuel cell air line, via a bypass line, which bypasses the additionalheat transfer device in the bypass air line, can be conducted into thefuel cell air line downstream of the residual gas heat transfer device.The residual gas heat transfer device can interact with the exhaust gasflow of the residual gas burner in order to heat up the fuel cell air.The additional heat transfer device can interact with the additionalburner in order to preheat the fuel cell air with the hot additionalburner exhaust gas. Should it be required to reduce or limit atemperature of the fuel cell, for example the temperature of theelectrolyte or a cathode temperature or an anode temperature in order toavoid overheating of the respective component of the fuel cell it is nowpossible subject to bypassing both heat transfer devices to supplycooling air sucked in from the surroundings while bypassing both heattransfer devices to the fuel cell on the cathode side. This is madepossible with the help of the bypass line, which connects the bypass airline to the fuel cell air line between the two heat transfer devices.

It is to be understood that the fuel cell system with the system batteryeven as such belongs to the scope of this invention.

It is noted, furthermore, that a reformer with a heating jacket of saidtype for a fuel cell system of this type also belongs to the scope ofthis invention as such. The reformer can additionally comprise a mixingjacket and/or an evaporator space of said type.

It is to be understood that the features mentioned above and still to beexplained in the following cannot only be used in the respectivecombination stated but also in other combinations or by themselveswithout leaving the scope of the present invention.

Preferred exemplary embodiments of the invention are shown in thedrawings and are explained in more detail in the following description,wherein same reference characters relate to same or similar orfunctionally same components. The various features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed to and forming a part of this disclosure. For a betterunderstanding of the invention, its operating advantages and specificobjects attained by its uses, reference is made to the accompanyingdrawings and descriptive matter in which preferred embodiments of theinvention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a circuit diagram-like and highly simplified embodiment of anarrangement with a fuel cell system and electrical loads; and

FIG. 2 is a circuit diagram-like and highly simplified embodiment of afuel cell system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in particular, FIG. 1 shows an arrangement 0having a fuel cell system 1, which can be arranged in a motor vehicle orin any other mobile or stationary application as a sole or additionalelectrical source of energy, with a fuel cell 2 and a residual gasburner 3. The fuel cell 2 during operation generates electric currentfrom anode gas and cathode gas, which can be tapped off via electrodes4. The fuel cell 2 is preferably configured as a SOFC-fuel cell. Theresidual gas burner 3 during operation converts anode exhaust gas withcathode exhaust gas, generating burner exhaust gas in the process. Theconversion in this case can be effected with an open flame. A catalyticconversion is likewise conceivable.

An anode exhaust line 5 connects an anode side 6 of the fuel cell 2,which comprises at least one anode 95, to the residual gas burner 3. Acathode exhaust line 7 connects a cathode side 8 of the fuel cell 2,which comprises at least one cathode 104, to the residual gas burner 3.In a combustion chamber 9 of the residual gas burner 3, the conversionof the fuel cell exhaust gases then takes place. The residual gas burner3 can form a structurally integrated unit with the fuel cell 2. Theanode exhaust line 5 and the cathode exhaust line 7 are then internallines or paths.

In the fuel cell 2, an electrolyte 10 separates the anode side 6 fromthe cathode side 8. The supply of anode gas to the anode side 6 of thefuel cell 2 takes place via a reformer gas line 11 or an anode gas line11. The supply of cathode gas to the cathode side 8 of the fuel cell 2takes place via a fuel cell air line 12. The cathode gas is preferablyair. A burner exhaust line 13 discharges the burner exhaust gasgenerated by the residual gas burner 3 from the residual gas burner 3 orfrom its combustion chamber 9. In this burner exhaust line 13, aresidual gas heat transfer device 14 is incorporated, which additionallyis incorporated in the fuel cell air line 12. The residual gas heattransfer device 14 generates a media-separated heat-transferringcoupling between the fuel cell air line 12 and the burner exhaust line13. The residual gas heat transfer device 14 in this case can bestructurally integrated in the residual gas burner 3.

In the example, the fuel cell system 1 is equipped with a fuel cellmodule 15, which comprises the fuel cell 2, the residual gas burner 3and the residual gas heat transfer device 14. Furthermore, this fuelcell module 15 is equipped with a thermally insulating cover 16, whichencloses the components of the fuel cell module 15.

The fuel cell system 1 is additionally equipped with an air conveyingdevice 17, which can for example be a blower or a compressor or anelectrically operated turbocharger or a pump. During the operation, thisair conveying device 17 feeds air as cathode gas to the fuel cell 2 viathe fuel cell air line 12. The air conveying device 17 in this case ispart of an air supply module 18, which comprises its own thermallyand/or acoustically insulating cover 19, in which the air conveyingdevice 17 is arranged. The air conveying device 17 can preferentially beequipped with a filtering device 71 in order to filter particles and/oraerosols out of the conveyed air.

The fuel cell system 1 is additionally equipped with an additionalburner device 20 or an additional burner 20, which is configured so thatduring operation it converts air with an additional burner fuel orsimply fuel into additional burner exhaust gas. Said additional burnerexhaust gas in the process is discharged from the additional burner 20or from a combustion chamber 22 of the additional burner 20 via anadditional burner exhaust line 21 or briefly additional exhaust line 21.The additional exhaust line 21 preferentially contains a shut-off device67 for decoupling the additional burner 20 during a normal operation ofthe fuel cell system 1, during which the additional burner 20 isswitched off. The shut-off device 67 then functions as a non-returnvalve. In this additional exhaust line 21, an additional burner heattransfer device 23 or briefly additional heat transfer device 23 isincorporated. Apart from this, the additional heat transfer device 23 isincorporated in a bypass air line 24. The additional heat transferdevice 23 thus generates a media-separated, heat-transferring couplingbetween the additional exhaust line 21 and the bypass air line 24. Theadditional heat transfer device 23 in this case can be structurallyintegrated in the additional burner 20.

The bypass air line 24 bypasses the residual gas heat transfer device 14on the air side. For this purpose, the bypass air line 24 is connectedto the fuel cell air line 12 on the inlet side via a tapping point 25between the air conveying device 17 and the residual gas heat transferdevice 14. On the outlet side, the bypass air line 24 is connected tothe fuel cell air line 12 via an input line 26 between the residual gasheat transfer device 14 and the fuel cell 2. A first portion of the fuelcell air line 12, which leads from the air conveying device 17 to theinput point 26 is designated 12′ in the following, while a secondportion of the fuel cell air line 12 leading from the input point 26 tothe fuel cell 2 or to the cathode side 8 is designated 12″ in thefollowing.

According to the embodiment shown here, a bypass line 72 can beoptionally provided, which connects a tapping point 73 of the bypass airline 24 arranged upstream of the additional heat transfer device 23 tothe input point 26, i.e. to the fuel cell air line 12. This bypass line72 because of this makes possible bypassing the additional heat transferdevice 23 within the bypass air line 24. A first portion of the bypassair line 24, which leads from the tapping point 25 as far as to thefurther tapping point 73, is designated 24′ in the following, while asecond portion of the bypass air line 24 leading from the furthertapping point 73 as far as to the input point 26 is designated 24″ inthe following. For controlling the bypass line 72, a further valve 74can be provided, which in the example is practically arranged on thefurther tapping point 73.

During the normal operation of the fuel cell system 1, i.e. with theadditional burner 20 switched off, preheating of the fuel cell air takesplace exclusively via the residual gas heat transfer device 14. Incertain operating situations it can be required to avoid a furthertemperature increase of the fuel cell 2 or achieve a cooling of the fuelcell 2. This can be required for example in order to protect a componentof the fuel cell 2, such as for example the electrolyte 10, fromoverheating. The respective temperature or the fuel cell 2 can beregulated through cold ambient air, which is fed to the fuel cell air inorder to reduce the temperature of the latter. The cold ambient air inthis case can be fed to the second portion 12″ of the fuel cell air line12 via the bypass air line 24, wherein the bypass air line 24 bypassesthe residual gas heat transfer device 14. If, however, during thestarting operation, the additional burner 20 is still active, theadditional heat transfer device 23 which is arranged in the bypass airline 24 also has to be bypassed in order to be able to achieve a coolingof the fuel cell air. The bypass line 72 is used for this purpose. Thecooling air then flows via the first portion 24′ of the bypass air line24 as far as to the bypass line 72 and from the bypass line 72 into thesecond portion 12′ of the fuel cell air line 12. Because of this, thecooling air on the one hand bypasses the residual gas heat transferdevice 14 and on the other hand the additional heat transfer device 23.

The supply of the additional burner 20 with air is carried out via anadditional air conveying device 27 and a corresponding air supply line28. The additional conveying device 27 can preferentially be equippedwith a filtering device 75, in order to filter particles and/or aerosolsout of the conveyed air. The air for the additional burner 20 in theprocess is preferably sucked in from surroundings 52 of the fuel cellsystem. The additional burner 20 is supplied with fuel with the help ofa fuel conveying device 29 via a suitable fuel line 30. The fuel can forexample be any hydrocarbons. However, a fuel with which for example aninternal combustion engine of the vehicle equipped with the fuel cellsystem 1 can also be operated is preferred. The fuel is thus diesel orbiodiesel or heating oil in particular. Petrol or natural gas or anybiofuel as well as synthetic hydrocarbons are also conceivable.Consequently, the fuel line 30 is practically connected to a fuel tank53 of the vehicle which is not shown in more detail here.

The additional burner 20 and the additional heat transfer device 23 inthis case are part of an additional burner module 31, which has its ownthermally insulating cover 32, in which the additional burner 20 and theadditional heat transfer device 23 are arranged. In addition, theadditional air conveying device 27 and the fuel conveying device 29 ofthe additional burner 20 in the example are part of the additionalburner module 31. These parts however are arranged outside theassociated cover 32.

In the shown example, the fuel cell system 1 is additionally equippedwith a reformer 33, which during the operation sub-stoichiometricallyconverts air during the operation with a reformer fuel or fuel, i.e. atan air ratio <1 and in the process generates hydrogen-containing andcarbon monoxide-containing reformat gas. This reformat gas as anode gasis fed to the anode side 6 of the fuel cell 2 via the reformat gas line11. To supply the reformer 33 with reformer air, a reformer air line 34is provided, which in this case is likewise fed by the air conveyingdevice 17. In the embodiment shown here, a further conveying device 35is arranged in the reformer air line 34 downstream of the air conveyingdevice 17, which in the following is described as reformer air conveyingdevice 35. With the help of this reformer air conveying device 35, theair fed to the reformer 33 can be brought to an elevated pressure level.In addition, this reformer air conveying device 35 can be configured asa hot gas conveying device. For example, it can be configured in themanner of a blower, compressor, electrically operated turbocharger or ofa pump.

To supply the reformer 33 with fuel, a fuel conveying device 36 isprovided, which supplies a suitable fuel to the reformer 33 via asuitable fuel line 37. This, in turn, can be any hydrocarbon. Preferredis the fuel which is also supplied to the internal combustion engine ofthe vehicle equipped with the fuel cell system 1. Accordingly, the fuelline 37 provided for supplying the reformer 33 is practically alsoconnected to the tank 53 of the vehicle.

The reformer 33 contains a combustion chamber 38 or mixing chamber 38,in which the reformer air and the fuel are mixed and combusted. Thereformer 33 additionally contains a catalytic converter 40, with thehelp of which the reformat gas can be generated with the help of partialoxidation.

The reformer 33 is part of a reformer module 41, which comprises aseparate or own thermally insulating and/or gas-tight cover 42, in whichthe reformer 33 is arranged. In the example, the reformer fuel conveyingdevice 36 belongs to the reformer module 41. However, said conveyingdevice 36 for this purpose is arranged outside the cover 42 of thereformer module 41.

The burner exhaust line 13 or briefly exhaust line 13 contains anoxidation catalytic converter 43 downstream of the residual gas heattransfer device 14 for the exhaust gas retreatment. In the exhaust line13, a heating heat transfer device 44 can be additionally incorporated,which during the operation can heat up a fluid flow 45 indicated by anarrow. This can be an air flow 45, which is fed to a vehicle interiorwhich is not shown here. Alternatively, the fluid flow 45 can also be acoolant of a cooling circuit, wherein the cooling circuit contains aheat transfer device for heating an air flow, which can then beconducted for example to the vehicle interior. The heating heat transferdevice 44 in this case is practically arranged downstream of theoxidation catalytic converter 43. Because of this, the heat which in theoxidation catalytic converter 43 is liberated if appropriate during theconversion of pollutants can be utilized for heating the vehicleinterior.

The tapping point 25, at which the bypass air line 24 branches off thefuel cell air line 12, is practically configured as a valve or arrangedon a valve 46. This valve 46 makes possible for example quasi anydistribution of the air flow conveyed by the air conveying device 17over the portion of the fuel cell air line 12 conducted through theresidual gas heat transfer device 14 and over the bypass air line 24.The valve 46 is practically part of a valve device 47, which via adistribution strip 48, distributes the air conveyed by the air conveyingdevice 17 on the pressure side over the fuel cell air line 12 and overthe reformer air line 34. For controlling the air rate fed to thereformer 33, a further valve 49 can be provided, which can likewisebelong to the valve device 47. Furthermore, a cooling gas line orcooling air line 50 is provided in the example, via which cooling aircan be fed to the residual gas burner 3. The cooling air line 50 iscontrollable with a valve 51, which in the example likewise belongs tothe valve device 47. The air conveying device 17 likewise sucks the airfrom the surroundings 52 of the fuel cell system 1 via a suction line53. The valve device 47 in the example is likewise a part of the airsupply module 18 and arranged within the associated cover 19.

The valves of the valve device 47 and the air conveying devices 17, 35are preferably temperature-controlled or temperature-regulated. Forexample, the valve 49, the conveying device 17 and the reformer airconveying device 35 are regulated dependent on the temperature of themixing chamber 38 and/or depending on the temperature of the catalyticconverter 40. The valve 51 and the air conveying device 17 can beregulated for example dependent on the temperature of the combustionchamber 9. The valve 46 and the air conveying device 17 can for examplebe regulated dependent on the temperature of the cathode side 8. The airconveying device 35 can for example be regulated dependent on thetemperature of the mixing chamber 38 and/or dependent on the temperatureof the catalytic converter 40.

The electrical current generated with the help of the fuel cell system 1practically serves for supplying electrical loads with electric currentor with electrical energy. In this case, the arrangement 0 comprises aload system 54, which comprises a load network battery 82 and firstloads 78, which is electrically supplied via a load network voltage ofthe load network battery 82. The arrangement 0 can for example be partof a vehicle, in particular of a motor vehicle. In this case, the loadsystem 54 for example corresponds to the vehicle's electrical system 54while the load network battery 82 corresponds to an electrical systembattery 82 of the vehicle. The load network voltage of the load networkbattery 82 is at a load network voltage level, which in the case of avehicle can for example amount to 12V. The first loads 78 are forexample control units, light bulbs and a radio of the vehicle.

On the electrodes 4 of the fuel cell 2, a cell voltage at a cell voltagelevel can be tapped off. The cell voltage level in the shown embodimentis for example around 42V and can, in particular dependent on a loadingof the fuel cell 2, fluctuate for example between 36V and 60V. The cellvoltage level however can have any value in particular dependent on thetype and the loading of the fuel cell 2.

The fuel cell system 1 is additionally equipped with an energy storageunit 56 designed as a system battery 56, across which there is a systemvoltage at a system voltage level, wherein the system voltage level forexample has a value of 24V. The system battery 56 in particular servesthe purpose of storing the cell voltage generated by the fuel cell 2 oran electrical energy connected therewith. To this end, a charging device79 is electrically connected to the system battery 56. Supplying thecell voltage of the fuel cell 2 to the system battery 56 or to thecharging device 79 is effected via a voltage converter device 57 of thefuel cell system 1. The voltage converter device 57 to this end isarranged between the fuel cell 2 and the system battery 56 or thecharging device 79 and is electrically connected to these. In order torender the cell voltage of the fuel cell 2 suppliable to the systembattery 56, the voltage converter device 57 converts the cell voltage atthe cell voltage level to the system voltage which is on the lowersystem voltage level. The voltage converter device 57 thus converts forexample the cell voltage of 42V into a voltage of 24V, which correspondsto the system voltage. In order to render the system voltage across thesystem battery 56 also suppliable to the fuel cell 2, in particular tothe electrodes 4 and to the anode 95 of the fuel cell 2, the voltageconverter device 57 is additionally designed accordingly. In this case,the voltage converter device 57 is able if required to convert thesystem voltage at the system voltage level into another voltage inanother voltage level, subsequently supplying it to the fuel cell 2.This serves the purpose of protecting in particular the anode 95 fromoxidation. The oxidation in this case is particularly relevant inoxidizing conditions on the anode side 6, wherein the fuel cell system 1on the one hand can comprise a device for determining the relevantconditions and on the other hand is preferentially designed in such amanner that the electrical voltage to be present across the electrodes 4is regulatable.

The system voltage across the system battery 56 is additionallysuppliable to system loads 80 of the fuel cell system 1. This means thatthe system battery 56 functions as an electrical buffer or as anelectrical storage unit, via which the electrical supply of system loads80 is effected. System loads 80 are for example the conveying devices17, 27, 29, 35, 36, the valves 46, 49, 51, 67, 74, 76 as well asignition devices such as for example glow pins and sparkplugs, withwhich in the residual gas burner 3, in the additional burner 20 and inthe reformer 33 a combustion reaction can be initiated. Likewise, acontrol device 55, with the help of which the individual components ofthe fuel cell system 1, for example as a function of temperatures,pressures, electrical currents etc. of the fuel cell system, can beactuated, represent a system load 80 of the fuel cell system 1, whereinthe system loads 80 are operated at the system voltage level, i.e. forexample at 24V. The electrical energy of the system battery 56 stored inthe form of the system voltage can be utilized in particular forstarting the fuel cell system 1 without external electrical energy orvoltage supply.

In order to render the system voltage across the system battery 56 alsosuppliable or utilizable for the load system 54, in particular for theload network battery 82 of the load system 54, a load voltage converter77 is additionally provided, which converts the system voltage of thesystem battery 56 at the system voltage level to the vehicle'selectrical system voltage or load network voltage at the load networkvoltage level, supplying it to the load network battery 82. In the shownembodiment, the load network voltage level is lower than the systemvoltage level. The load voltage converter 77 is consequently designed asa step-down converter and reduces the system voltage level to the loadnetwork voltage level. To supply first loads 78 of the load system 54with the system voltage, a charging device 79 is additionally arrangedon the load network battery 82, wherein the charging device 79 in theshown example is integrated in the load network battery 82. The loadnetwork battery 82 thus functions similarly to the system battery 56 asa buffer or storage unit, via which an electrical supply of the firstloads 78 is effected. The cell voltage generated by the fuel cell 2 andthe system voltage across the system battery 56 and the system networkvoltage of the load system 54 are usually d.c. voltages. This means thatthe polarity of these voltages does not change over time. Practically,the voltage converter device 57 and the load voltage converter 77 eachcomprise a d.c. voltage converter 83.

To supply electrical secondary loads 84, 85, which are operated with anadditional voltage on at least one additional voltage level, through thesystem battery 56, at least one additional voltage converter 86 isadditionally provided. In the shown embodiment, two additional voltageconverters 86′, 86″ are provided, which convert the system voltage levelto two different additional voltage levels, wherein both additionalvoltage levels are higher than the system voltage level. The additionalvoltage converters 86′, 86″ are thus designed as step-up converters 86′,86″.

The first additional voltage converter 86′ converts the system voltageof the system battery 56 on the system voltage level to the firstadditional voltage on the higher first additional voltage level. Assecondary loads 84, in particular external electrical loads, for examplea refrigerator, a cooler box, a TV set and a coffee maker which usuallyrequire an additional voltage level of 110V or 220V and are additionallyoperated with an a.c. voltage are mentioned here. To this end, the firstadditional voltage converter 86′ comprises an inverter 87. The firstadditional voltage converter 86′ thus additionally converts the d.c.voltage-like system voltage of the system battery 56 into the a.c.voltage-like first additional voltage in addition to increasing thesystem voltage to the first additional voltage level, making this a.c.voltage-like first additional voltage available to the relevantelectrical secondary loads 84.

The second additional voltage converter 86″ converts the system voltageof the system battery 56 on the system voltage level into a secondadditional voltage level, wherein the thus converted voltage for examplecorresponds to a high voltage, i.e. a voltage higher than 300V. Thus,the second additional voltage level is higher than the first additionalvoltage level of the first additional voltage converter 86′. Assecondary loads 85 on the second additional voltage level made availableby the second additional voltage converter 86″, air-conditioningdevices, in a vehicle therefore in particular an air-conditioning systemof the vehicle, are electrically supplied for example.

The additional exhaust line 21 in the embodiments shown here isconnected to the exhaust line 13 via an input point 60, namelydownstream of the residual gas heat transfer device 14. In this case,this input point 60 is practically positioned so that it is locatedupstream o the oxidation catalytic converter 43. Because of this, theresidual heat of the additional burner exhaust gas can be utilized forheating up the oxidation catalytic converter 43. At the same time, theresidual heat of the additional burner exhaust gas can be utilized forheating the heating heat transfer device 44.

The fuel cell system 1 comprises a reformer supply device 88, which iscoupled to the reformer 33 in a heat-transferring manner. This heattransfer is realized via an inflow 89 of the reformer supply device 88,a heating jacket 90 through which a flow can flow and a return 91 of thereformer supply device 88. In this case, the inflow 89 on the one end isconnected to the additional exhaust line 21 upstream of the additionalheat transfer device 23 and on the other end is fluidically connected tothe heating jacket 90 via a first opening 97 of the heating jacket 90.The heating jacket 90 is designed in a manner to allow a through- flowand is coupled to the reformer 33 in a heat-transferring manner. Inaddition, the heating jacket 90 is fluidically separated or isolatedfrom the reformer 33. The through-flow capable heating jacket 90additionally comprises a cavity which is fluidically connected to thefirst opening 97. The additional burner exhaust gas conducted via theinflow 89 from the additional exhaust line 21 to the heating jacket 90thus flows through the first opening 97 into the heating jacket 90, inparticular into the cavity of the heating jacket 90, without enteringthe reformer 33 in the process. Furthermore, the return 91 of thereformer supply device 88 is fluidically connected to the heating jacket90 on the one end through a second opening 98 of the heating jacket 90and on the other end is fluidically connected to the additional exhaustline 21 downstream of the additional heat transfer device 23. Theadditional burner exhaust gas of the additional burner 20 which flowedthrough the inflow 89 into the heating jacket 90, in particular into thecavity of the heating jacket 90, consequently flows through the return91 of the reformer supply device 88 back to the additional exhaust line21. Thus, the heating jacket 90, in particular the cavity of the heatingjacket 90, is subjected to the through-flow of warm additional burnerexhaust gas and the heat of the additional burner exhaust gas of theadditional burner 20 transferred to the reformer 33. A shut-off device94 for decoupling the additional burner 20 from the heating jacket 90during the normal operation of the fuel cell system 1 is additionallyarranged in the inflow 89.

The heating jacket 90 surrounds the reformer 33 in the region of thecatalytic converter 40. The first opening 97 of the heating jacket 90is, as is visible in the section of FIG. 2, arranged on the side of theheating jacket 90 facing away from the mixing chamber 38, while thesecond opening 98 is arranged on the side of the heating jacket 90facing the mixing chamber 38, so that the additional burner exhaust gascirculates in the heating jacket 90 and has as long as possible a flowpath. The mixing chamber 38 is surrounded by a mixing jacket 92 adjacentto the heating jacket 90. The mixing jacket 92 comprises a cavity and isfluidically connected to the reformer air line 34 on its side facingaway from the reformer 33, while on its side facing the reformer 33 itcomprises mixing jacket outlets 99, which fluidically connect the mixingjacket 92 to the mixing chamber 38. Thus, the reformer air flows via themixing jacket 92 into the mixing chamber 38 of the reformer 33, whereinin the mixing jacket 92 a preconditioning can take place. An evendistribution of the mixing jacket outlets 99 along the circumference ofthe mixing jacket 92 additionally ensures the even inflow of thereformer air in the mixing chamber 38.

The reformer 33 shown here furthermore comprises an evaporator space 93,which is fluidically connected to the fuel line 37. Accordingly, thefuel flows via the evaporator space 93 into the mixing chamber 38,wherein the evaporator space 93 serves the purpose of evaporating themostly liquid fuel prior to entering the mixing chamber 38. Theevaporator space 93, the mixing chamber 38 and the catalytic converter40 are consequently fluidically interconnected.

Additionally or alternatively, a branch 100 branched off the additionalexhaust line 21 can be coupled to an end plate 101 of the fuel cell 2 ina heat-transferring manner. In the shown example, the branch 100 isconnected to a tapping point 102 arranged on the valve 94 of the inflow89 and conducts the additional burner exhaust gas to the end plate 101and subsequently back to the return 91 of the reformer supply device 88via an input point 103, by way of which the additional burner exhaustgas returns into the additional exhaust line 21. It is thus possible toalso heat the fuel cell 2 with the help of the additional burner 20. Thetapping point 102 arranged on the valve 94 in this case allows quasi anydistribution of the additional burner exhaust gas for heating thereformer 33 or the fuel cell 2.

The fuel cell 2 can typically have a stack-like structure, in which amultiplicity of plate-like fuel cell elements are stacked on top of oneanother and because of this form a fuel cell stack or stack. On itsends, the fuel cell stack is closed off through two end plates, namelythrough said end plate 101 and through a further end plate. This furtherend plate in the example comprises an anode gas connection 61, to whichthe anode gas line 11 or reformat gas line 11 is connected, a cathodegas inlet 62, to which the cathode gas line 12 or fuel cell air line 12is connected, an anode exhaust gas outlet 63, to which the anode exhaustline 5 is connected, and a cathode exhaust gas outlet 64, to which thecathode exhaust line 7 is connected. Since all educt connections arethus arranged on this further end plate, this can also be described asconnection plate. In contrast with this, the other end plate 101 merelyforms a termination of the fuel cell stack, so that it can also bedescribed as termination plate.

In another embodiment, a further cover can be arranged in the thermallyinsulating cover 16 of the fuel cell module 15, which in particular isconfigured gas-tight. This inner cover can likewise have a thermallyinsulating effect. It is likewise conceivable to configure the outercover 16 in a gas-tight manner. Furthermore, a cover can be sufficientif it is configured thermally insulating and gas-tight. It is nowpossible, in particular, to connect the previously mentioned branch 100of the additional exhaust line 21 to an interior space of the fuel cellmodule 15 enclosed by the inner cover. In this case, the branch 100opens into the said interior space at an entry point and exits from theinterior space again at a distal exit point. Because of this, the fuelcell module 15 can be heated with the additional burner exhaust gas. Inparticular, this can be combined with the heating of the fuel cell 2.For example, the additional burner exhaust gas can be initiallyconducted via the branch 100 as far as to the termination plate and fromthe latter exit into the interior space in order to be discharged againfrom the interior space via the exit point.

The fuel cell system 1, in the preferred embodiment shown here, isfurthermore equipped with a recirculation line, which is connected onthe input side to the anode exhaust line 5 and on the output side to thereformer air line 34 via an input point 66, namely upstream of thereformer air conveying device 35. Since the recirculated anode exhaustgas during the operation of the fuel cell system 1 can havecomparatively high temperatures, the reformer air conveying device 35 ispractically configured for being exposed to hot gases, wherein thesegases can be additionally toxic and/or explosive.

The valve device 47 in the example is configured in order to distributethe air sucked in by the air conveying device 17 over the fuel cell airline 12, the bypass air line 24, the cooling air line 50 and thereformer air line 34.

In another embodiment which is not shown, the air conveying device 17via the valve device 47 can be additionally used for supplying theadditional burner 20 with air. For this purpose, the additional burnerair line 28 can be connected to a distribution strip 48 via a furthervalve. Alternatively, the additional air conveying device 27 in theadditional burner air line 28 can also be omitted.

Additionally to the preheating of the fuel cell air with the help of theadditional burner 20, a residual gas circulation in a circulationcircuit 68 can also be realized during a cold start of the fuel cellsystem 1, in which the reformer 33 in particular also is at an ambienttemperature, which circulation circuit 68 is indicated in FIG. 1 by aninterrupted line.

Furthermore, an additional bypass line 69 is provided, which branchesoff the reformat gas line 11 and bypasses the anode side 6 of the fuelcell 2. Because of this it is possible to heat up the reformer 33 byprotecting the material, without there being the risk of the anode 95being damaged through residual oxygen from the reformer 33. In theexample, this bypass line 69 is connected to the anode exhaust line 5,so that reformer exhaust gas is again introduced into the original pathupstream of the residual gas burner 3. The bypass line 69 can becontrolled with a corresponding valve 70. Practically, the bypass line69 to this end is designed so that its flow resistance is lower than theflow resistant of the anode side 6 of the fuel cell 2. With open valve70, the reformer exhaust gas, following the path of least resistance,then does not flow through the anode side 6, but through the bypass line69. In this version, the reformer 33 can be easily operatedover-stoichiometrically, since contacting of the anode side 6 withresidual oxygen in the reformer exhaust gas need not be expected. Thisquasi random over-stoichiometric operation mode of the reformer 33simplifies the starting operation of the reformer 33, in particular formaintaining lower temperatures.

FIG. 2 shows the fuel cell 2 of a fuel cell system 1. In order toprotect electrodes 4 and the anode 95 from oxidation, the system voltageacross the system battery 56 can be supplied to the fuel cell 2. In thiscase, the system voltage is applied to the fuel cell 2 in such a mannerthat a negative pole of the system battery 56 is electrically connectedto the anode side 6 or the anode 95, while a positive pole of the systembattery 56 is electrically connected to the cathode side 8 or thecathode 104. In addition, the respective electrical connections are notrealized necessarily directly. In the present example this means thatthe voltage converter device 57 and the charging device 79 are connectedbetween the system battery 56 and the electrodes 4. Such a supply of thesystem voltage to the fuel cell 2 functions as protective voltage, whichis supplied to the fuel cell 2 when required, i.e. in particular inoxidizing conditions on the anode side 6. This can for example becontrolled by means of a switch 96, which in particular is controlled bythe control device 55, and establishes a corresponding electricalconnection and a concomitant electric flow of an associated electriccurrent S when required.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

1. An arrangement comprising: a fuel cell system; and an electrical loadsystem, wherein: the load system is for the electrical supply of firstloads and comprises a load network battery with a load network voltageat a network load voltage level; the fuel cell system comprises a fuelcell for generating an electrical cell voltage at a cell voltage level;the fuel cell system is for supplying electrical system loads of thefuel cell system comprises a system battery with a system voltage at asystem voltage level; the network load voltage level and the systemvoltage level are different; the fuel cell system comprises a voltageconverter device for converting the cell voltage level to the systemvoltage level and/or of the system voltage level to the cell voltagelevel; for supplying electrical secondary loads at least one additionalvoltage converter for adapting the system voltage across the systembattery to at least one additional voltage level is provided; the systemvoltage level and the additional voltage level are different; forsupplying the load system at least one load voltage converter foradapting the system voltage across the system battery to the loadnetwork voltage level is provided.
 2. The arrangement according to claim1, wherein the voltage converter device comprises at least one d.c.voltage converter.
 3. The arrangement according to claim 1, wherein theat least one additional voltage converter comprises at least oneinverter.
 4. The arrangement according to claim 1, wherein the loadvoltage converter comprises at least one d.c. voltage converter.
 5. Thearrangement according to claim 1, wherein the arrangement comprises anelectrical charging device for charging the system battery by means ofthe electrical cell voltage generated by the fuel cell.
 6. Thearrangement according to claim 5, wherein the charging device isarranged between the fuel cell and the system battery.
 7. Thearrangement according to claim 1, wherein the system voltage across thesystem battery is suppliable via the voltage converter device as aprotective voltage to electrodes of the fuel cell.
 8. The arrangementaccording to claim 7, wherein the protective voltage is regulatabledependent on thermodynamic parameters on an anode side of the fuel cell.9. The arrangement according to claim 1, wherein at least one secondaryload level is at a domestic level, in particular at 220V or 110V. 10.The arrangement according to claim 1, wherein the arrangement is part ofa motor vehicle.
 11. The arrangement according to claim 10, wherein theload system is an electrical system of the vehicle and the load networkbattery is a network battery of the vehicle.
 12. The arrangementaccording to claim 1, wherein the arrangement is part of a stationarysystem.
 13. A fuel cell system comprising: a fuel cell generating anelectrical cell voltage at a cell voltage level, the fuel cell systemfor supplying electrical system loads of the fuel cell system; a systembattery with a system voltage at a system voltage level; a connection toan electrical load system, wherein the load system is for the electricalsupply of first loads and comprises a load network battery with a loadnetwork voltage at a network load voltage level, wherein the networkload voltage level and the system voltage level are different; a voltageconverter device for converting the cell voltage level to the systemvoltage level and/or of the system voltage level to the cell voltagelevel; an additional voltage converter for adapting the system voltageacross the system battery to at least one additional voltage level forsupplying electrical secondary loads, wherein the system voltage leveland the additional voltage level are different; and a load voltageconverter for adapting the system voltage across the system battery tothe load network voltage level for supplying the load system.
 14. Thefuel cell system according to claim 13, further comprising: a reformer;a reformer supply device; a burner for generating burner exhaust gas,wherein the heat of the burner exhaust gas can be transferred to thereformer of the fuel cell system by means of the reformer supply device.15. The fuel cell system according to claim 14, wherein the reformercomprises a heating jacket and a mixing jacket, wherein the heatingjacket surrounds the reformer in the region of a catalytic converter ofthe reformer while the mixing jacket surrounds the reformer in theregion of a mixing chamber.